KR20080031615A - Radio communication method, transmitter, and receiver - Google Patents

Abstract

A wireless communication method, a transmitter, and a receiver are provided to selectively carry out precoding transmission(beamforming) and MIMO(Multi Input Multi Output) communication according to various wireless environments, thereby obtaining communication quality such as propagation reaching ranges and transmission capacities capable of maintaining communication reliability. Among plural antenna groups consisting of plural antennas which are portions of respective transmission antennas(15-1 to 15-Nt) and plural antennas which are portions of respective reception antennas(21-1 to 21-Nr), an antenna group which satisfies the first selection standard regarding communication quality is selected. Among combinations of transmission and reception antennas which constitute the selected antenna group, a combination which satisfies the second selection standard regarding communication quality is selected, and communication is performed by using a portion of or the overall selected combination of the transmission and reception antennas. A spatial multiplexing modulator(11) performs mapping and modulation of the coding sequence obtained by means of necessary error coding into symbols having signal points of such as a predetermined modulation scheme. A precoding processor(12) performs precoding of Ns-number(1<=Ns<=Nr) of transmission data streams by using the precoding matrix or the code word given by a precoding matrix/code word selector(17). The precoding processor maps the transmission data streams to Lt-number of transmission antennas selected by a transmission antenna selection controller(18), thereby performing beam forming by Lt-number of transmission antennas.

Description

Wireless communication methods and transmitters and receivers {RADIO COMMUNICATION METHOD, TRANSMITTER, AND RECEIVER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication method, a transmitter, and a receiver, and more particularly, to a technique for selecting a transmit / receive antenna in a wireless system using MIMO (Multiple Input Multiple Output).

In recent years, MIMO (Multiple-Input Multiple-Output) has attracted attention as a technology that enables high-capacity (high speed) data communication by effectively utilizing a frequency band. MIMO transmits a data stream independent from a plurality of antennas of a transmitter by using a plurality of antennas, i.e., a transmitter having a plurality of antennas and a receiver having a plurality of antennas, and receiving signals at each receiving antenna of the receiver. The plurality of transmission signals (data streams) mixed together on the propagation path are individually separated from each other using channel state information (also referred to as channel estimates) indicating the state (environment) of the communication path (channel). By separating, it is a technique of improving the transmission rate without requiring the expansion of the frequency band.

In the MIMO communication system, a plurality of antennas are generally employed on the base station apparatus (BS) side than on the mobile station apparatus (MS) side. In some cases, the BS and the MS communicate with each other via a relay station (RS) in order to ensure transmission quality and the like.

In a conventional MIMO system (see Patent Document 1 below), in order to secure a transmission capacity, the reception antennas of the BS are grouped, and the BS performs reception using an antenna group selected based on a criterion among them.

In addition, in the technique of Patent Document 2 below, the number of transmission antennas of the BS is small, so that when the transmission antenna is selected, it is possible with a certain amount of calculation.

[Patent Document 1] Japanese Patent Application Laid-Open No. 2004-312381

[Patent Document 2] Japanese Patent Application Laid-Open No. 2006-67237

However, the conventional method (the technique of Patent Document 1) discloses only the configuration in which the BS selects a reception antenna, and neither discloses nor suggests a configuration in which the BS selects a transmission antenna.

In addition, in the technique of Patent Document 2, as the number of antennas of the BS increases, it takes a long time to find the optimal antenna.

In the prior art, the number of transmit / receive antennas used (selected) on the BS (transmitter) side and the MS (receiver) side is usually the same number (for example, 2 BS 2 MIMO 2x2 MIMO, etc.). Therefore, depending on the communication environment, the condition of the antenna may be unsatisfactory, and it is difficult to secure a robust transmission capacity.

In addition, when the number of antennas of the RS increases, using all of the antennas of the BS side and the RS side simultaneously increases the cost, complexity, and the like. In addition, when antenna selection is performed between the BS and the RS, since the number of antennas is very large, it takes a very long time to find an optimal antenna.

The present invention was made in view of the above problems, and an object of the present invention is to enable an optimal transmission antenna and a reception antenna to be selected at a higher speed and with a smaller amount of computation than in the related art.

In addition, it is also an object to selectively perform MIMO communication and precoding transmission (beam forming) according to a wireless environment so as to secure communication quality such as transmission capacity and radio wave coverage that can maintain communication reliability. It is done.

In order to achieve the above object, the present invention is characterized by using the following wireless communication method, transmitter and receiver.

That is, (1) In the wireless communication method of the present invention, in a wireless communication system in which wireless communication is performed between a transmitter having a plurality of transmitting antennas and a receiver having a plurality of receiving antennas, a plurality of any one of the plurality of transmitting antennas is part of the above. And an antenna group that satisfies a first selection criterion for communication quality from among a plurality of antenna groups of any of the respective reception antennas, and a combination of a transmission antenna and a reception antenna constituting the selected antenna group. Among them, a combination that satisfies the second selection criterion for communication quality is selected, and the communication is performed using part or all of the combination of the selected transmit antenna and receive antenna.

(2) Here, each of the transmission antennas constituting the antenna group is preferably a plurality of transmission antennas equidistant from a plurality of adjacent transmission antennas or reference transmission antennas.

(3) In addition, some of the transmission antennas constituting an arbitrary antenna group may overlap as components of different antenna groups.

(4) The number of transmitting antennas constituting the antenna group may be larger than the number of receiving antennas constituting the antenna group.

(5) Further, in the above combination, it is determined whether there is a combination that satisfies the criteria for MIMO communication by the number of receiving antennas and the same number of transmitting antennas, and when it is determined, the transmitting antennas of the combination are determined. If it is determined that there is no MIMO communication by use, and it is determined that it does not exist, the precoding transmission may be performed by using all of the combination of transmission antennas.

(6) In addition, some or all of the receiving antennas constituting an arbitrary antenna group may overlap as components of different antenna groups.

(7) The receiver may also notify the transmitter of information on the combination of the selected transmit antenna and receive antenna.

(8) The radio communication method of the present invention, N _t transmitters and, N _r pieces having a transmitting antenna (N _t is an integer of 2 or more) between the receiver with a receiving antenna of the (N _r is an integer of 2 or greater) a N _t × N _r of the channel estimation value obtained in the wireless communication system for performing wireless communication, for between each transmit antenna and each receive antenna at, L _t × L _r items (where, L _t <N _t, L _r Group is classified into a plurality of blocks consisting of an element estimate value, and a block satisfying the first selection criterion about communication quality is selected from the plurality of blocks, and a second selection about communication quality is selected from a combination of element estimate values of the selected block. A combination that satisfies a criterion is selected, and the communication is performed using some or all of a combination of a transmission antenna and a reception antenna corresponding to the combination of the selected element estimates.

(9) Further, the receiver of the present invention, N _t transmitters and, N _r pieces having a transmitting antenna (N _t is an integer equal to or greater than two) wireless between a receiver with a receiving antenna of the (N _r is an integer of 2 or greater) a receiver in a wireless communication system which performs communication, the N _t × N _r of the channel estimation value obtained for between the transmission antennas and the reception antennas, L _t × L _r items (where, L _t <N _t, Grouping means for grouping into a plurality of blocks consisting of element estimates of L _r ≤ N _r ), and block selecting means for selecting a block that satisfies a first selection criterion for communication quality among the plurality of blocks obtained by the grouping means. And element estimation value selection means for selecting a combination that satisfies the second selection criterion for communication quality among the combinations of the element estimates of the blocks selected by the first selection means, and the block selection means or the yaw. And characterized in that on the basis of the selection result by the estimation value selecting means it includes a notifying means which generates antenna selection information for the transmitter notifies the transmitter.

(10) In addition, the transmitter of the present invention has N _t (N _t is an integer of 2 or more) transmitting antennas and performs wireless communication between the receivers according to the above (9), wherein the antenna from the notification means And receiving means for receiving selection information, and antenna selecting means for selecting a use transmitting antenna in accordance with the antenna selection information received by the receiving means.

According to the above invention, any one of the effects or advantages described below can be obtained.

(1) Because of the large number of transmit antennas, even if the number of transmit / receive antennas becomes very large (i.e., the number of element estimates in the channel matrix becomes very large), the selection of an optimal transmit antenna and a receive antenna suited to a wireless environment at a high speed with a smaller amount of computation than in the past By doing so, it is possible to realize optimum communication in accordance with the wireless environment. Moreover, cost, complexity, etc. can also be reduced.

(2) If there is a combination of transmit / receive antennas satisfying the antenna selection criteria of the predetermined (the first and the second), MIMO communication is performed by the transmit / receive antenna of the combination, and suitable for MIMO communication (the second antenna selection criterion is applied). If there is no satisfactory combination of transmit / receive antennas, precoding transmission (beam forming) can be performed, thereby ensuring communication quality such as transmission capacity and radio wave coverage that can always maintain communication reliability in any wireless environment. can do.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings. However, this invention is not limited to the following embodiment, Of course, a various deformation | transformation can be implemented in the range which does not deviate from the meaning of this invention.

[A] Description of First Embodiment

1 is a block diagram showing the configuration of a multi-antenna wireless communication system according to a first embodiment of the present invention. The wireless communication system shown in FIG. 1 includes a base station apparatus (BS 10) serving as at least one transmitter. And a mobile station apparatus (MS 20) as at least one receiver, and the BS 10 is, for example, the spatial multiplex modulator 11, the precoding processor 12, L _t (L _t is an integer greater than or equal to 2) number of transmitting RF units 13-1 to 13-L _t (hereinafter, denoted as transmitting RF unit 13 when not distinguished), antenna switch 14, , N _t (N _t is an integer of 2 or more, N _t ≥ L _t ) Tx antennas 15-1 to 15-N _t (hereinafter referred to as Tx antenna 15 if not distinguished) and codebook And a memory 16, a precoding matrix / codeword selector 17, and a transmit antenna selector 18.

On the other hand, when the MS 20 pays attention to the main part, for example, N _r (N _r is an integer of 2 or more) reception antennas 21-1 to 21-N _r (hereinafter, the reception antennas are not distinguished). (21)) and N _r (L _r is an integer of 2 or more, L _r ≤ N _r ) receiving RF units 23-1 to 23-L _r (hereinafter, the receiving RF unit if not distinguished) (23), the MIMO received signal processor 24, the channel estimator 25, the antenna selector (used antenna determiner) 26, the codebook memory 28, the precoding matrix A calculation / codeword retrieval section 29 is provided. In addition, that the number of receiving RF units 23 is N _r means that the number of receiving data streams that can be processed at one time by the MS 20 (the receiving RF unit 23) is N _r , so the maximum value thereof is described above. As is N _r .

(Configuration description of the BS 10)

Here, in the BS 10, the spatial multiplex modulator 11 uses a predetermined modulation scheme, for example, Quadrature Phase Shift Keying (QPSK) or QAM ( Mapping and modulating a symbol (signal of a data channel) having a signal point such as Quadrature Amplitude Modulation), for example, N _s (where 1≤N _s ≤min (L _t , N _r )) transmission data streams This is to be obtained. In addition, in this spatial multiplex modulation 11, a known signal (pilot signal or preamble signal) and control information are transmitted between the BS 10 and the MS 20 used for channel estimation in addition to the data channel signal. Multiple processing such as a control channel signal (control symbol) can also be performed.

Precoding processing (pre-coding means) 12, by using the precoding matrix (matrix) or the code word supplied from the precoding matrix / code word selector (17), _s N (1≤N ≤N _{s r} ), The beamforming by the L _t transmit antennas 15 is performed by precoding the Tx transmit data streams and mapping them to the L _t transmit antennas 15 selected by the transmit antenna selection control unit 18 as described below. To do. However, the precoding (beam forming) is performed when the number of transmission data streams N _s <the number of selective transmission antennas L _t (i.e., selectively depending on the number of selective transmission antennas) as described later. In the case of N _s = the number of selective transmit antennas L _t , it is controlled so as not to be implemented to perform MIMO multiplexing.

The transmission RF unit 13 performs a given radio transmission process including digital conversion (DA) conversion, frequency conversion (upconversion) to radio frequency (RF), and the like, for each of the L _t transmission data streams. The switch 14 selects the L _t transmission antennas 15 to be used for transmission under the control of the transmission antenna selection control unit 18 and connects them with the transmission RF unit 13. The radiating RF signal from the transmitting RF unit 13 connected through the antenna switch 14 is radiated toward the MS 20 in the space.

The codebook memory 16 memorizes in advance the codebook (codeword) used when determining the precoding matrix (or vector, hereinafter, identical) used in the precoding. The codebook is defined, for example, as a set of predetermined unitary matrices (the elements are defined as codewords), and the number of data streams N _s , the number of transmit antennas L _t and the number of feedback bits ( Is determined based on L). In addition, an element in the codebook is defined as a codeword. Since it is necessary to use the same codebook between the MSs 20, the same thing is stored in advance on the MS 20 side (codebook memory 28).

Therefore, the BS 10 does not have to notify (feedback) all the element information of the precoding matrix obtained based on the CSI from the MS 20, but the limited information (for example, the index of the codeword in the codebook). ), It becomes possible to determine the precoding matrix to use based on the information. Such a limited information notification method is called limited feedback transmission, and it is possible to achieve effective use of the uplink band from the MS 20 to the BS 10.

In addition, in this example, limited information such as the index is transmitted using a feedback channel indicated by 40 in FIG. 1. The feedback channel 40 is one of the uplink channels from the transmission system of the MS 20 to the reception system of the BS 10. In FIG. 1, the transmission system and the BS 10 of these MS 20 are shown. The illustration of the receiving system is omitted.

Next, the precoding matrix / codeword selector 17 receives the antenna index (antenna selection information) notified from the MS 20 by the feedback channel 40 and notifies the antenna selection control unit 18. In addition, since the precoding matrix required for the precoding is supplied to the precoding processing unit 12, the precoding matrix notified from the MS 20 by the feedback channel 40 may be supplied as it is at that time. A codeword specified from the index notified by the limited feedback transmission may be selected from the codebook and a precoding matrix corresponding thereto may be supplied.

The transmission antenna selection control unit 18 controls the antenna switch 14 in accordance with the antenna selection information to control the connection between the transmission RF unit 13 and the transmission antenna 15.

(Configuration description of the MS 20)

In the MS 20, the reception antenna 21 receives RF signals transmitted from the transmission antenna 15 of the BS 10, respectively, and the reception RF unit 23 receives the reception antenna 21, respectively. For a received RF signal in, a given radio reception process including frequency conversion (down conversion) to baseband frequency, analog to digital (AD) conversion, and the like is performed.

The MIMO received signal processor 24 separates, demodulates, and decodes the received signal (digital baseband signal), that is, the spatially multiplexed received signal, processed by the received RF unit 23 for each transmission data stream. In addition, the said separation process is a method which uses the inverse of a channel correlation matrix, for example based on CSI calculated | required by the correlation operation of the said pilot signal (or a preamble signal. Hereinafter, it is the same) and a pilot replica, The method may be performed by using a method such as a maximum likelihood detection (MLD) algorithm.

The channel estimator 25 obtains the CSI (ie, estimates a channel response) by a correlation operation between the pilot signal processed by the reception RF unit 23 and the pilot replica held by the MS 20 in advance. .

The use antenna selection unit 26 selects (determines) a combination of the transmission antenna 15 and the reception antenna 21 used for communication with the BS 10 based on predetermined antenna selection criteria. Hierarchical selection, that is, grouping the transmitting antenna 15 and the receiving antenna 21 into a plurality of antenna groups consisting of a plurality of transmitting antennas 15 and a plurality of receiving antennas 21, wherein the first antenna group among the antenna groups An antenna group satisfying the antenna selection criterion is selected, and a combination of the transmitting antenna 15 and the receiving antenna 21 satisfying the second antenna selection criterion is selected from among the selected antenna group.

In addition, when the number of transmission antennas N _t is smaller than a certain reference number, all antenna combinations may be selected. In addition, some or all of the receiving antennas 21 may be an element common to each antenna group. When all are made into a common element, it corresponds to grouping only the transmission antenna 15 into plural groups.

Such group classification means to classify the element estimates of the CSI (channel matrix) obtained by the channel estimator 25, and selects a combination of the transmitting antenna 15 and the receiving antenna 21 from among the antenna groups. To do means to select a combination of element estimates of the channel matrix. Details of the group classification, antenna selection criteria, and the like will be described later.

That is, the use antenna selector 26 of the present example comprises N _r × N _t channel estimates obtained between each transmission antenna 15 and each reception antenna 21 as L _r × L _t element estimates. It has a function as a grouping means for grouping into a plurality of blocks.

As described above, the codebook memory 28 stores the same codebook as the BS 10 side in advance, and the precoding matrix calculation / codeword retrieval unit 29 obtains the CSI obtained by the channel estimation unit 25. On the basis of the BS 10, and generates information (feedback information) necessary for the precoding on the BS 10 side and informs the BS 10 by the feedback channel 40, and calculates the precoding matrix calculated based on the CSI, or In the case of the limited feedback transmission, an index of the codeword obtained by searching the codebook in the codebook memory 28 can be generated as the feedback information.

(System operation explanation)

Hereinafter, the operation of the MIMO communication system of the present embodiment configured as described above, particularly the operation focusing on the antenna selection method, will be described in detail with reference to FIGS. 2 to 5.

First, as shown in FIG. 5, the BS 10 and the MS 20 transmit information about the number of transmit / receive antennas, the processing capability of the data stream, and the like in advance, so that the number of antennas and the processing capability of the communication partner are mutually transmitted. (Step S11, S21).

The BS 10 transmits the pilot signal to the MS 20 (step S12), and the MS 20 performs a correlation calculation between the received pilot signal and the pilot replica in the channel estimator 25. The channel response is estimated (CSI is obtained) (step S22).

The MS 20 selects one antenna group that satisfies a predetermined antenna selection criterion based on the obtained CSI. That is, each transmit antenna 15 of the BS 10 is grouped into a plurality of antenna groups such that the number of transmit antennas L _t per group is larger than the number of receive antennas L _r usable on the MS 20 side. And one antenna group satisfying the antenna selection criteria is selected from the antenna groups.

In this group classification, for example, as shown schematically in FIG. 2, the adjacent L _t transmit antennas 15 may be a group, and as shown schematically in FIG. 4, The L _t transmit antennas 15 at equal intervals (equal distance) may be used as one group as a certain transmit antenna 15 as a reference antenna.

If the number of transmit antennas N _t = 9 of the BS 10, the number of receive antennas N _r = L _r = 2, and the number of transmit antennas L _t = 3 per antenna group are shown in FIG. As shown in Fig. 3, the group classification includes 18 element estimates (h _ij : i = 1 to 2, j = 1 to 9) of the channel matrix obtained as a matrix of L _r × N _t = 2 × 9. Is equivalent to grouping into three blocks (2 × 3 matrix H _s ) consisting of adjacent element estimates of L _r × L _t = 2 × 3 (= 6), thus selecting an antenna group, It is equivalent to selecting a block that satisfies the antenna selection criterion in the corresponding block unit.

By the same theory, the group classification as shown in Fig. 4 is a block composed of 2 x 3 = 6 element estimates equidistant from the channel matrix obtained as a matrix of L _r x N _t = 2 x 9 (channel matrix). H _s ) means grouping. In this case, communication (multi-user MIMO transmission) for a plurality of MSs 20 in one antenna group is possible.

As described above, the method of selecting element estimate values constituting one block (matrix H _s ), that is, the method of group classification of antenna groups, may be considered in various ways in addition to the above. For example, element estimate values belonging to a certain block may be different. It is also possible to classify the groups so that they belong to duplicates. However, in order to make the computation amount as small as possible, it is preferable to perform simple group classification as shown in FIG. 2 (FIG. 3) or FIG. 4.

First, the MS 20 (used antenna determination unit 26) assumes any of the antenna selection criteria shown in (a) to (c) below, again on the premise of group classification as described above. In other words, first, the antenna group (block of element estimation values) is selected using the first antenna selection criterion regarding the communication quality between the BSs 10. That is, the use antenna determination unit 26 has a function as a block selection means for selecting a block that satisfies any one antenna selection criterion in the following (a) to (c) among a plurality of blocks of the element estimate value. .

(a) Capacity selection criteria

The MS 20 (used antenna determination unit 26) selects an antenna group that maximizes the communication capacity (Capacity) between the BSs 10 by the following equation (1).

In Equation (1), H _s is a channel matrix of an antenna group, ρ is an average signal to noise ratio (SNR) of each receiving antenna 21 in the corresponding antenna group, and det is a determinant, H _s ′ Represents a plural conjugate transpose of H _s .

(b) Singular value selection criteria

The MS 20 (used antenna determination unit 26) maximizes the minimum singular value λmin {H _s } of the channel matrix H _s by using Equation (2) below (which is the minimum SNR). Select the antenna group.

(c) Condition Number Selection Criteria

The MS 20 (used antenna determination unit 26) calculates the maximum singular value λmax {H _s } of the channel condition number, that is, the channel matrix H _s , according to the following equation (3): Choose an antenna group that minimizes the division by _s } (which means optimizing the error rate).

First, when the antenna group is selected as described above, the MS 20 (used antenna determination unit 26) then determines the number of transmit antennas and the number of receive antennas in the selected antenna group, as shown in FIG. In comparison, it is determined whether the number of transmitting antennas L _t and the number of receiving antennas L _r are the same (step S24).

As a result, if identical, the MS 20 transmits the index of the selected transmission antenna 15 to the BS 10 by the feedback channel 40 by the precoding matrix calculation / codeword retrieval unit 29 (notification). (Step S25 from the "YES" route in step S24).

On the other hand, if the number of transmitting antennas L _t and the number of receiving antennas L _r are not the same, that is, the number of transmitting antennas L _t > the number of receiving antennas If L _r (the number of data streams N _s ), the used antenna determination unit 26 adjusts the number of transmit antennas L _t and the number of receive antennas L _r in the same number, and then transmits and receives all transmission / reception in the selected antenna group. The antenna combination is searched for, and a judgment is made as to whether a predetermined antenna selection criterion (second antenna selection criterion based on communication quality) is satisfied (e.g., what threshold is below the number of conditions of the channel) (step S26). , S27).

In addition, for adjustment (selection) of the number of transmission / reception antennas to be the target of the judging, for example, the signal-to-interference and noise power ratio (SINR) of each antenna 15, 21 is calculated, and the antenna has the minimum SINR. This may be performed by excluding (15, 21) or by selecting antennas 15, 21 having a large SINR or an average power.

As a result, when the antenna selection criterion is satisfied, the MS 20 uses the precoding matrix calculation / codeword search unit 29 to determine the index of the selected transmission antenna 15 in the feedback channel (similar to step S25). 40, it transmits (notifies) to BS 10 (step S28 from the "YES" route of step S27).

That is, the use antenna determination unit 26 has a function as element estimation value selection means for selecting a combination that satisfies the second selection criterion regarding communication quality among the combinations of the element estimates of the blocks selected by the block selection means described above. And the selection means further functions as a judging unit for determining whether, among the combinations of the element estimates, there is a combination that satisfies the criteria for MIMO communication by the number of receiving antennas and the same number of transmitting antennas 15. Equipped.

In addition, the precoding matrix calculation / codeword retrieval unit 29 obtains antenna selection information for the BS 10 based on the selection result by the use antenna determination unit 26 (block selection means or element estimate value selection means). It has a function as a notification means for generating and notifying the BS 10.

On the other hand, when the antenna selection criteria are not satisfied, the use antenna determination unit 26 further determines whether or not the eigenmode transmission is performed (from step S29 to step S29). As a result, when it is determined that the used antenna determination unit 26 performs eigenmode transmission, the MS 20 decomposes the singular values of the CSI (channel matrix) by the precoding matrix calculation / codeword search unit 29. (Singular Value Decomposition: SVD) is calculated to obtain a precoding matrix (details will be described later), and it is transmitted to the BS 10 by the feedback channel 40 (from step S30 from the example path of step S29).

On the other hand, when it is determined that the use antenna determination unit 26 does not perform the eigenmode transmission (that is, the limited feedback transmission), the MS 20 performs the precoding matrix calculation / codeword search unit 29. The codebook memory 28 retrieves the index of the codeword in the codebook, and transmits the index of the codeword to the BS 10 via the feedback channel 40 (step No from the step S29). S31).

That is, the precoding matrix calculation / codeword retrieval unit 29 (notification means) determines that the antenna selection information (antenna index) according to the combination is determined when the determination unit determines that there is a combination of the element estimate values. If it is determined that the information is not present in the determination unit, the precoding information (precoding matrix or index of the codeword) required for the precoding transmission by the BS 10 is based on the combination factor estimation value. It also has a function as an antenna selection information generation unit that generates as antenna selection information and notifies the BS 10.

On the other hand, in BS 10, MIMO multiplexing is performed by the precoding matrix / codeword selector 17 based on the antenna index notified by the feedback channel 40 from the MS 20 in step S25 or S28 above. It is determined whether to transmit or not (step S13). In other words, the precoding matrix / codeword selector 17 determines that MIMO multiplexing is performed when the number of transmission data streams N _s = the number of selective transmission antennas L _t .

As a result, when it is determined that MIMO multiplexing is performed, the BS 10 controls the antenna switch 14 by the transmitting antenna selection control unit 18, and transmit antenna 15 specified by the notified antenna index. The transmission RF unit 13 existing in the transmission data stream is connected, and MIMO multiplex transmission is performed (from step S14 to step S14).

On the other hand, if it is determined that the MIMO multiplex transmission is not performed, the BS 10 (precoding matrix / codeword selector 17) determines whether or not to perform eigenmode transmission (step S13 from "no" root). S15). As a result, when it is determined in step S15 that the precoding matrix is notified from the MS 20 by the feedback channel 40 and the eigenmode transmission is performed, the precoding matrix / codeword selector 17 corresponds to the corresponding. The precoding matrix is supplied to the precoding processor 12. In addition, the antenna switch 14 is controlled by the transmit antenna selection control unit 18 so that the transmit RF unit 13 in which the transmit data stream exists and the selected transmit antenna 15 (the number of transmit antennas in this case is MS ( 20) is greater than the number of receive antennas selected).

As a result, the BS 10 performs beamforming by the precoding using the transmission antenna 15 larger than the number of reception antennas (transmission data streams) on the MS 20 side to perform transmission to the MS 20. (YES from the route of step S15, step S16).

On the other hand, when it is determined in step S29 that the index of the codeword is notified by the feedback channel 40 from the MS 20 and the limited feedback transmission is performed instead of the eigenmode transmission, the precoding matrix / codeword selector The code 17 retrieves the corresponding codebook from the codebook memory 16 based on the index of the codeword, determines the precoding matrix based on the codebook, and supplies the codebook to the precoding processor 12. In addition, as in the case of the eigen mode transmission, the antenna switch 14 is controlled by the transmit antenna selection control unit 18 so that the transmit RF section 13 in which the transmit data stream exists and the selected transmit antenna 15 (the Also in this case, the number of transmit antennas is larger than the number of receive antennas selected on the MS 20 side).

As a result, the BS 10 performs beamforming by the precoding using the transmission antenna 15 larger than the number of reception antennas (transmission data streams) on the MS 20 side to perform transmission to the MS 20. (Step S17 from the NO route of step S15).

That is, when the precoding information (precoding matrix or codeword) is received as the antenna selection information from the precoding matrix / codeword selecting section 17, the precoding processing section 12 based on the precoding information, Precoding transmission is performed by the transmitting antenna 15 corresponding to the combination of the element estimates.

In addition, when each transmission antenna 15 in one antenna group of BS 10 does not overlap with respect to several MS 20 (for example, as shown in FIG. 2 above), each MS 20 may be referred to. Can be simultaneously transmitted, and when some or all of the transmitting antennas 15 in one antenna group of the BS 10 are duplicated for the plurality of MSs 20, the overlapping transmitting antennas 15 In this case, time division transmission may be performed.

In the case of TDD (Time Division Duplex), the channel information can be measured by sounding from the BS 10 and the MS 20 from the correlation of the channels. In the case of FDD (Frequency Division Duplex), the BS 10 can grasp downlink channel information by the feedback from the MS 20 to the BS 10.

In addition, periodically or irregularly, the BS 10 transmits the reception quality information of the MS 20 which the BS 10 has grasped to the MS 20, and re-executes the hierarchical antenna selection and precoding process described above as necessary. In this case, it is possible to adapt to the latest radio wave environment.

(Description of Precoding Process)

Next, not only the precoding process (beam forming) but also the details of the eigenmode transmission and the limited feedback transmission will be described.

(Unique mode transmission)

When the complete CSI is known between the BS 10 and the MS 20, the precoding matrix calculation / codeword search unit 29 of the MS 20 performs singular value decomposition (SVD) and decomposes the CSI. The obtained matrix is obtained as a precoding matrix.

For example, when N _s transmission data streams, L _t transmission antennas 15, L _r reception antennas 21, and N _s ≤ min (L _t , L _r ), CSI (channel matrix H) Is a matrix of L _r × L _t , and when H is singly resolved, it is represented by the following equations (4) and (5).

U represents a left-side specific matrix, V represents a right-side specific matrix, and D represents a diagonal matrix, and the elements λ ₁ ,. λ _m is proportional to the gain of the eigen mode. The gain of the intrinsic mode is ordered and has a gain in which the first intrinsic mode lambda ₁ is maximum and the mth intrinsic mode lambda _m is minimum. m represents the rank of the channel matrix H.

And when precoding is performed, the optimal precoding matrix is the N _s column on the left side of the right singularity matrix V (indicated by V ₁ : N _s ). Accordingly, the precoding processing unit 12 of the BS 10 uses the precoding matrix F = V ₁ : N _s to convert L _s transmission data streams into L _t transmission antennas according to the following equation (6). 15).

Here, s denotes an N _s × 1 transmit data vector, and x denotes an L _t × 1 transmit antenna data vector.

Therefore, the reception side y can express the received signal y by the following formula (7).

Where n represents a noise vector of L _r × 1. In addition, y represents the reception signal of the L _r × 1, the signal of each reception antenna 21 is the overlap of a transmission signal. y, H, F are known in the MS 20, and the transmission signal

In the following equation (8), the maximum likelihood (ML) method can be applied to obtain the equation. However, since the complexity is enormous, a linear decoder having a small complexity as shown by the following equation (9) or equation (10) is employed. It is desirable to.

Q [] represents a demapper, and G represents a matrix of N _s × L _r .

In other words, when a ZF (Zero Forcing) linear decoder is applied, G in Equation (8) can be represented by Equation (9) below.

However, () ⁺ represents a matrix pseudo-inverse.

In the case of applying a Minimum Mean Square Error (MMSE) linear decoder, G in Equation (8) may be represented by Equation (10) below.

However, () ^-1 represents matrix inversion.

(Send limited feedback)

The principle of limited feedback transmission is described below.

In advance, the same codebook is determined between the transmitting side BS 10 and the receiving side MS 20 based on the number of transmission data streams N _s , the number of transmission antennas L _t , and the number of feedback bits L. . As already explained, it is assumed that the BS 10 and the MS 20 each store the same codebook in the codebook memories 16 and 28 and are known.

In the MS 20, the channel estimation unit 25 performs channel estimation, obtains the CSI, and based on the CSI, for example, an optimal code based on any of the criteria shown in the following (1) to (3). Select a word.

(1) Minimum Mean Square Error (MMSE) Selection Criteria

Mean Square Error (MSE) used by the MS 20 (precoding matrix calculation / codeword retrieval unit 29) is known as H and F, and can be expressed by the following equation (11).

The precoding matrix calculation / codeword retrieval section 29 selects a codeword from the codebook which minimizes Trace (tr) or Determinant (det) of the MSE of the equation (11). That is, it is selected by the following formula (12) or formula (13).

(2) Capacity selection criteria

The MS 20 (precoding matrix calculation / codeword retrieval unit 29) can select a codeword from among the codebooks to maximize the capacity by the following equation (14).

(3) Singular value selection criteria

The MS 20 (precoding matrix calculation / codeword search section 29) may select a codeword from among the codebooks to maximize a minimum singular value.

Then, the MS 20 (precoding matrix calculation / codeword search unit 29) transmits the index (L bit) of the codeword selected based on the above criteria from the feedback channel 40 to the BS 10. do.

As a result, the BS 10 uses the matrix (or vector) as the precoding matrix using the corresponding codebook based on the received index as described above. In addition, in the case of the limited feedback transmission, a linear decoder (ZF linear decoder or MMSE linear decoder) may be applied as in the eigen mode.

As described above, according to the present embodiment, the transmitting antenna 15 on the BS 10 side and the receiving antenna 21 on the MS 20 side are converted into the plurality of transmitting antennas 15 and the plurality of receiving antennas 21. A transmit antenna 15 and a receive antenna, which are grouped into a plurality of antenna groups, select an antenna group satisfying a first antenna selection criterion from each antenna group, and satisfy the second antenna selection criterion among the selected antenna group ( Since the combination of 21) is selected, even if the number of transmit / receive antennas is very large (i.e., the number of element estimates of the channel matrix is very large), in particular, since the number of the transmit antennas 15 on the BS 10 side is large, the amount of computation is smaller than before. In this way, the optimum transmission antenna 15 and the reception antenna 21 can be selected at high speed to meet the wireless environment, thereby achieving optimum communication in response to the wireless environment. Moreover, cost, complexity, etc. can also be reduced.

In addition, if there are combinations of transmit and receive antennas that are grouped so that the number of transmit antennas is larger than the number of receive antennas in one antenna group, and that satisfies the predetermined (first and second) antenna selection criteria, If MIMO communication is performed at the transmit / receive antenna, and there is no combination of transmit / receive antennas suitable for MIMO communication (satisfied with the second antenna selection criterion), precoding (beam forming) using more transmit antennas 15 than the number of receive antennas is performed. In any wireless environment, it is possible to secure communication quality such as transmission capacity and radio wave coverage that can always maintain communication reliability.

In addition, when the BS 10 receives a signal from the MS 20, not all the receiving antennas are used, but the antenna group is selected, thereby improving performance by maximum ratio combining (MRC). can do.

[B] Description of Second Embodiment

Fig. 6 is a block diagram showing the configuration of a multi-antenna wireless communication system according to a second embodiment of the present invention. The wireless communication system shown in Fig. 6 includes at least one base station apparatus (BS) 10 and at least It is comprised including one relay (relay) station apparatus (RS) 30, BS 10 is comprised similarly to 1st Embodiment, and when RS 30 pays attention to the main part, it is N, for example. _r (N _r is an integer of 2 or more) receiving antennas 31-1 to 31-N _r (hereinafter, referred to as receiving antenna 31 if not distinguished), antenna switch 32, and L _r (L _r is an integer of 2 or more, L _r ≤ N _r ) RF receiving units 33-1 to 33-L _r (hereinafter, referred to as receiving RF unit 33 if not distinguished) and MIMO reception Signal processor 34, channel estimator 35, antenna selector (used antenna determiner) 36, antenna selector 37, codebook memory 38, precoding matrix calculation / code Woah It is constructed by comprising a search unit (39).

That is, although the RS 30 of this example has a structure substantially the same as the MS 20 shown in FIG. 1, it is provided with the antenna switch 32 and the receiving antenna selection control part 37, and the receiving antenna used ( It is possible to select 31).

That is, the antenna switch 32 connects the arbitrary reception antenna 31 and the arbitrary reception RF part 33 according to control from the reception antenna selection control part 37, and the reception antenna selection control part 27 is The reception antenna 31 and the reception RF unit 33 determined (selected) by the use antenna selection unit 36 are connected and controlled by the same procedure as in the first embodiment.

In addition, the reception antenna 31, the reception RF unit 33, the MIMO reception signal processing unit 34, the channel estimation unit 35, the use antenna determination unit 36, the reception antenna selection control unit 37, and the codebook 38 The precoding matrix calculation / codeword retrieval unit 39 is each of the reception antenna 21, the reception RF unit 23, the MIMO received signal processing unit 24, and the channel estimating unit 25 described above in the first embodiment. The same or the same as the use antenna selection unit 26, the reception antenna selection control unit 27, the codebook 28, and the precoding matrix calculation / codeword search unit 29.

However, in this example, when the BS 10 communicates with the RS 30, not all the receiving antennas 31 on the RS 30 side are components of one antenna group, but, for example, as shown in FIG. As shown in the figure, the classification of the reception antenna 31 is also performed. Also in this case, as shown in FIG. 2 or FIG. 4, neighboring or equidistant antennas can be grouped as components of one antenna group in the BS 10 and the RS 30, respectively. Also in this example, a part of the transmitting antenna 15 or the receiving antenna 31 constituting one antenna group may overlap as a component of another antenna group. The number of transmit antennas on the BS 10 side that constitutes one antenna group is preferably larger than the number of receive antennas on the RS 30 side.

Assuming such group classification, in this example as well, according to the first embodiment, hierarchical antenna selection is performed to select an optimal combination of transmit and receive antennas suitable for a wireless environment, and to perform MIMO communication or precoding. Beam forming is performed.

That is, the RS 30 selects an antenna group that satisfies the first antenna selection criterion from the antenna groups by the use antenna determination unit 36 based on the CSI obtained from the channel estimator 35. Among the antenna groups, a combination of a transmit antenna 15 and a receive antenna 31 that satisfy the second antenna selection criterion is selected. If there is a combination of the same number of transmitting antennas 15 and receiving antennas 31, MIMO transmission is performed. Otherwise, precoding (beam) is performed using all the transmitting antennas 15 in the selected antenna group. Foaming).

More detailed operation is the same as in steps S11 to S17 and S21 to S31 in which the MS 20 is replaced with the RS 30 in FIG. 5. In the RS 30, however, when the antenna index is transmitted to the BS 10 in step S25 or S28, the reception antenna selection control unit 37 is notified by notifying the reception antenna selection control unit 37 of the selected reception antenna 31. 37, connection control between the selective reception antenna 31 and the reception RF section 33 is performed.

As described above, the antenna selection procedure similar to that of the first embodiment also applies to the communication between the BS 10 and the RS 30, so that it is possible to achieve a high-speed and optimal wireless environment with a smaller amount of computation than in the prior art. By selecting the transmitting antenna 15 and the receiving antenna 31, it is possible to realize the optimum communication for the wireless environment. Moreover, cost, complexity, etc. can also be reduced. Furthermore, according to the wireless environment, MIMO communication and precoding (beam forming) at the transmitting antenna 15 more than the number of receiving antennas are selectively performed, so that transmission capacity can always maintain the reliability of communication in any wireless environment. Communication quality such as radio wave coverage.

In addition, also in the communication between RS 30 and MS 20, when the antenna selection method applied by replacing BS 10 with RS 30 in the first embodiment is applied, the same operation as in the first embodiment The effect can be obtained.

Also in the present embodiment, when the BS 10 receives a signal from the RS 30 or when the RS 30 receives a signal from the MS 20, not all receiving antennas are used. By selecting the antenna group, it is possible to improve the performance by maximum non-synthesis (MRC).

[C] bookkeeping

(Book 1)

A wireless communication system for performing wireless communication between a transmitter having a plurality of transmitting antennas and a receiver having a plurality of receiving antennas,

An antenna group that satisfies a first selection criterion for communication quality is selected from a plurality of antenna groups, each of which is a part of each of the transmission antennas and a plurality of which of each of the reception antennas,

From among combinations of the transmitting antenna and the receiving antenna constituting the selected antenna group, a combination satisfying the second selection criterion about communication quality is selected,

And performing the communication using some or all of the selected combinations of transmit and receive antennas.

(Supplementary Note 2)

Each transmission antenna constituting the antenna group is a plurality of transmission antennas equidistant from a plurality of adjacent transmission antennas or reference transmission antennas.

(Supplementary Note 3)

A part of the transmitting antennas constituting an arbitrary antenna group is overlapped as a component of a different antenna group, wherein the radio communication method according to Appendix 1 or 2.

(Appendix 4)

The radio communication method according to any one of notes 1 to 3, wherein the number of transmitting antennas constituting the antenna group is larger than the number of receiving antennas constituting the antenna group.

(Supplementary Note 5)

Among the above combinations, it is determined whether there is a combination that satisfies the criteria for MIMO communication by the number of receiving antennas and the same number of transmitting antennas.

If it is determined to exist, MIMO communication is performed using the combination of transmission antennas,

When it is determined that there is no presence, the wireless communication method according to Appendix 4, wherein precoding transmission is performed using all of the combination of transmission antennas.

(Supplementary Note 6)

The radio communication method according to Appendix 1, wherein some or all of the reception antennas constituting an arbitrary antenna group are overlapped as components of different antenna groups.

(Appendix 7)

The wireless communication method according to Appendix 1, wherein the receiver notifies the transmitter of information on the combination of the selected transmit antenna and receive antenna.

(Appendix 8)

The group classification of the antenna group is determined based on the number of receiving antennas or the number of data streams that can be processed by the receiver.

(Appendix 9)

The wireless communication method according to Appendix 7, wherein at least the receiver notifies the transmitter of information on the number of the receiving antennas or the number of data streams.

(Book 10)

N _t pieces as a radio communication system performs radio communication between a receiver with a receiving antenna of the transmitter and the N _r dog (N _r is an integer of 2 or more) having a transmitting antenna (N _t is an integer of 2 or greater)

Group N _t x N _r channel estimates obtained between the respective transmit antennas and the respective receive antennas into a plurality of blocks consisting of L _t x L _r (L _t <N _t , L _r ) element estimates. Classify,

A block satisfying a first selection criterion about communication quality is selected from the plurality of blocks,

From the combination of element estimates of the selected block, a combination satisfying the second selection criterion about communication quality is selected,

And performing the communication using a part or all of a combination of a transmit antenna and a receive antenna corresponding to the combination of the selected element estimates.

(Appendix 11)

The wireless communication method according to any one of notes 1 to 10, wherein the transmitter is a base station apparatus and the receiver is a mobile station apparatus.

(Appendix 12)

The wireless communication method according to any one of notes 1 to 10, wherein the transmitter is a base station apparatus and the receiver is a relay station apparatus.

(Appendix 13)

The radio communication method according to any one of notes 1 to 10, wherein the transmitter is a relay station device and the receiver is a mobile station device.

(Book 14)

A receiver in a wireless communication system for performing wireless communication between a transmitter having N _t (N _t is an integer of 2 or more) transmitting antennas and a receiver having N _r (N _r is an integer of 2 or more) receiving antennas,

A plurality of N _t × N _r channel estimates obtained between the transmitting antennas and the receiving antennas are composed of L _t × L _r (where L _t <N _t , L _r ≤N _r ) element estimates. Grouping means for grouping into blocks;

Block selecting means for selecting a block that satisfies a first selection criterion about communication quality from among the plurality of blocks obtained by the grouping means;

Element estimate value selection means for selecting a combination that satisfies a second selection criterion for communication quality from among combinations of element estimates of blocks selected by the block selection means;

And notifying means for generating antenna selection information for the transmitter and notifying the transmitter on the basis of a selection result by the block selecting means or the required number of estimation value selecting means.

(Supplementary Note 15)

And the block comprises a plurality of element estimates equidistant from a plurality of adjacent element estimates or reference element estimates in a channel matrix of _Nt × N _r .

(Appendix 16)

The receiver according to Annex 14 or 15, wherein some element estimates in a block overlap as element estimates of different blocks.

(Appendix 17)

The receiver according to any one of notes 14 to 16, wherein L _t > L _r .

(Supplementary Note 18)

The element estimate value selecting means,

In addition to the combination of the element estimates, a determination unit for determining whether there is a combination that satisfies the criteria for MIMO communication by the number of receiving antennas and the same number of transmitting antennas is provided.

The notification means,

In the case where it is determined by the determination unit, the antenna selection information according to the combination is generated, and when it is determined that the determination unit does not exist, the precoding by the transmitter is based on the element estimate value of the combination. And the antenna selection information generation unit for generating precoding information necessary for transmission as the antenna selection information and notifying the transmitter.

(Appendix 19)

As the transmitter in a wireless communication system for performing wireless communication between a transmitter having N _t (N _t is an integer of 2 or more) transmission antennas and the receiver described in Appendix 14,

Receiving means for receiving the antenna selection information from the notification means;

And an antenna selecting means for selecting a used transmitting antenna according to the antenna selection information received by the receiving means.

(Book 20)

And, when the precoding information is received as the antenna selection information by the receiving means, further comprising precoding means for performing precoding transmission by a transmitting antenna corresponding to the combination of the element estimates, based on the precoding information. The transmitter according to Appendix 19.

1 is a block diagram showing the configuration of a multi-antenna wireless communication system according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining antenna grouping in the system shown in FIG. 1; FIG.

3 is a diagram for explaining grouping of a channel matrix corresponding to antenna grouping according to the first embodiment;

FIG. 4 is a schematic diagram for explaining another example of antenna grouping in the system shown in FIG. 1; FIG.

5 is a flowchart for explaining a system operation (antenna selection method) according to the first embodiment.

6 is a block diagram showing the configuration of a multi-antenna wireless communication system according to a second embodiment of the present invention.

FIG. 7 is a schematic diagram for explaining antenna grouping in the system shown in FIG. 6; FIG.

<Explanation of symbols for the main parts of the drawings>

10: base station unit (BS: Base Station)

11: Spatial Multiple Modulator

12: precoding processing unit

13-1 to 13-L _t : Transmission RF section

14: antenna switch

15-1 to 15-N _t : transmitting antenna

16: codebook memory

17: precoding matrix / codeword selector

18: transmission antenna selection control unit

20: mobile station device (MS: Mobile Station)

21-1 to 21-N _r : receiving antenna

23-1 to 23-N _r : reception RF unit

24: MIMO reception signal processing unit

25 channel estimation unit

26: antenna selection unit (use antenna determination unit)

28: codebook memory

29: precoding matrix calculation / codeword search unit

30: relay station device (RS: Relay Station)

31-1 to 31-N _r : receiving antenna

32: antenna switch

33-1 to 33-N _r : reception RF unit

34: MIMO reception signal processing unit

35 channel estimation unit

36: antenna selection unit (use antenna determination unit)

37: receiving antenna selection control unit

38: codebook memory

39: precoding matrix calculation / codeword search unit

40: feedback channel

Claims (10)

In a wireless communication system for performing wireless communication between a transmitter having a plurality of transmit antennas and a receiver having a plurality of receive antennas, An antenna group that satisfies a first selection criterion for communication quality is selected from a plurality of antenna groups including a plurality of any one of the transmission antennas and a plurality of any of the reception antennas, From among combinations of the transmitting antenna and the receiving antenna constituting the selected antenna group, a combination satisfying the second selection criterion about communication quality is selected, And performing the communication using some or all of the selected combinations of transmit and receive antennas. The method of claim 1, Each transmission antenna constituting the antenna group is a plurality of transmission antennas equidistant from a plurality of adjacent transmission antennas or reference transmission antennas. The method according to claim 1 or 2, A part of the transmitting antennas constituting an arbitrary antenna group is overlapped as a component of a different antenna group. The method according to claim 1 or 2, The number of transmitting antennas constituting the antenna group is larger than the number of receiving antennas constituting the antenna group. The method of claim 4, wherein Among the above combinations, it is determined whether there is a combination that satisfies the criteria for MIMO communication by the number of receiving antennas and the same number of transmitting antennas. If it is determined to exist, MIMO communication is performed using the combination of transmission antennas, And if not determined, precoding transmission using all of the combination of transmission antennas. The method of claim 1, A part or all of the receiving antennas constituting an arbitrary antenna group are overlapped as components of different antenna groups. The method of claim 1, And the receiver notifies the transmitter of information on the combination of the selected transmit antenna and receive antenna. In a wireless communication system performs radio communication between a receiver with a receiving antenna of a transmitter having a transmitting antenna, N _r dog (N _r is an integer of 2 or more) of N _t pieces (N _t is an integer of 2 or greater) Group N _t x N _r channel estimates obtained between the respective transmit antennas and the respective receive antennas into a plurality of blocks consisting of L _t x L _r (L _t <N _t , L _r ) element estimates. Classify, A block satisfying a first selection criterion about communication quality is selected from the plurality of blocks, From the combination of element estimates of the selected block, a combination satisfying the second selection criterion about communication quality is selected, And performing the communication using a part or all of a combination of a transmit antenna and a receive antenna corresponding to the combination of the selected element estimates. N _t pieces as the receiver in a radio communication system performs radio communication between a receiver with a receiving antenna of a transmitter having a transmitting antenna, N _r dog (N _r is an integer of 2 or more) of (N _t is an integer of 2 or greater) , A plurality of N _t × N _r channel estimates obtained between the transmitting antennas and the receiving antennas are composed of L _t × L _r (where L _t <N _t , L _r ≤N _r ) element estimates. Grouping means for grouping into blocks; Block selecting means for selecting a block that satisfies a first selection criterion about communication quality from among the plurality of blocks obtained by the grouping means; Element estimate value selection means for selecting a combination that satisfies a second selection criterion for communication quality from among a combination of element estimate values of blocks selected by the first selection means; Notification means for generating antenna selection information for the transmitter and notifying the transmitter based on a selection result by the block selection means or the element estimate value selection means Receiver comprising a. A transmitter having N _t (N _t is an integer of 2 or more) transmitting antennas and a radio communication system for performing wireless communication between the receiver of claim 9, Receiving means for receiving the antenna selection information from the notification means; Antenna selecting means for selecting a used transmitting antenna according to the antenna selection information received by the receiving means Transmitter comprising a.

Images